JPH0619263B2 - Surface roughness measuring device - Google Patents

Description

Detailed Description of the Invention a. TECHNICAL FIELD The present invention relates to a surface roughness measuring device using optical interferometry.

B. 2. Description of the Related Art For measuring surface roughness, a mechanical method using a stylus and a non-contact optical method are used. The method using a stylus is a destructive test because flaws are created by the stylus depending on the material of the object to be measured, and in many cases it cannot be used for inspection of products or intermediate products. Since the optical method is nondestructive, it is superior to the stylus method for product inspection, intermediate inspection, etc.

The optical cutoff method and the method that utilizes the speckle pattern that appears when the laser light is reflected on the object surface and radiated onto the screen are often used as the optical roughness measurement method. Since it is extremely sensitive to the movement of the sample, it is difficult to use it on the manufacturing site.

C. DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention is intended to provide an optical roughness measuring device that is not affected by the movement of a subject by taking advantage of the noncontact and nondestructive advantages of the optical roughness measuring method. is there.

D. Means for Solving Problems Optical means for coherently forming an image of the surface of the subject and an image of the reference surface or the surface of the subject itself, and interference formed by the overlapping of the two images. The roughness measuring device is constituted by a television image pickup means for picking up an image of the pattern by instantaneous exposure of the surface to be inspected and a data processing means for calculating the roughness corresponding value by analyzing the image data obtained by the image pickup means.

As a method of instantaneous exposure, a flash discharge tube of an electronic shutter is used, and the start of the closing operation of the electronic shutter and the start of the flash discharge tube are linked.

E. Action The television camera is configured to store and hold the photocurrent generated by the exposure of the light receiving surface for each pixel and to sequentially read the image data converted into the charge amount by this storing action by the scanning means, so that the sample surface is instantaneously read. Exposure, it is possible to capture an image of the interference pattern at that moment.
If μS, the amount of movement of the subject during that time is 0.1μ even if imaging is performed without stopping the subject transferred at a speed of 10 cm per second.
m, which is sufficiently smaller than the resolution of the optical system that forms an image of the surface of the subject. Then, by using an electronic shutter and a flash discharge tube as an exposure method, and by overlapping the listening characteristic range of the electronic shutter and the rising range of the light emission of the flash discharge tube, it is possible to block the light during the rising of the flash light emission, and the electronic shutter or It enables short-time exposure that cannot be achieved with a flash discharge tube alone. In the roughness measurement by the interferometry, the resolution in the direction perpendicular to the optical axis of the optical system, that is, the surface of the subject is extremely high and is on the order of Å. Therefore, it is suitable for the roughness measurement of this order. Up and down movement of articles during transfer is caused by the vibration of the transfer device.
Considering a vibration with an amplitude of 0.01 mm at 000 Hz (when a high-pitched sound such as a can is transmitted to the measurement position due to an object hitting the frame of the transfer device), the maximum vertical movement during 1 μS is approximately It is 600 Å, and it is possible to measure the roughness of about 0.1 μm. Furthermore, when Sharinda interference is used that causes the surface image of the same object to be overlapped with the surface image of the same object, vertical movement of the object may occur. However, since the two images move exactly the same, the interference pattern is not affected at all, and the sensitivity of roughness measurement is dramatically improved.

F. Embodiment FIG. 1 shows an embodiment of the present invention. Reference numeral 1 is a subject, which is transported by the conveyor C in the direction of the arrow. An objective lens 2 forms an enlarged image of the surface of the subject 1 on the light receiving surface of the CCD cell 10. Reference numeral 3 denotes a plane semi-transparent mirror that is inserted between the objective lens 2 and the surface of the subject 1 so as to be orthogonal to the optical axis of the objective lens 2. A high reflectance coating 4 is formed at the center of the lower surface of the objective lens 2. I am doing it. Therefore, the light of the light source 6 is divided into upper and lower parts by the semitransparent mirror 3, and the light reflected upward is reflected at the center of the lower surface of the objective lens 2 and again reflected upward by the semitransparent mirror 3. With this configuration, an image of the central portion of the lower surface of the objective lens 2 is also formed on the light receiving surface of the CCD 10. That is, the interferometer shown in the figure forms the image of the surface of the subject 1 and the image of the reference surface on the light receiving surface of the CCD 10 in a coherent manner with the lower surface of the objective lens 2 as the reference surface.

Reference numeral 6 is a strobe flash tube as a light source, and the light emission time is 1.5 μS. The light from the light source 6 passes through the filter F, is condensed on the diaphragm 7 by the condenser lens 8, and is reflected by the beam splitter 5 in the optical axis direction of the objective lens 2. An object detector 12 is a reflective photoelectric switch, which detects passage of the object and sends a detection signal to the CPU. When the CPU receives this detection signal, it sends a command signal to the power supply circuit 9 of the light source 6, and the flash tube 6 of the light source.
Light up. In this way, the CCD cell 10 holds the interference pattern between the surface of the subject 1 and the reference surface 4 below the objective lens 2 as a charge signal. CPU after the light source 6 has finished emitting light
Sends a scanning signal to the CCD cell 10, sends the image data of the interference pattern to the memory 11 via the A / D converter and stores it in the same memory, and the memory 11 is stored until the next object is sent. Data is read out, data processing is performed, a roughness display value is calculated, and output to the printer 12 for printing.

FIG. 2 shows an embodiment of a structure for particularly shortening the exposure time on the subject surface. The optical system may be the same as that shown in FIG. 1 and is omitted in the figure. 101 is an image tube and a is a photocathode on which an interference pattern is formed. The image tube converts a light image into a photoelectron image on the photocathode a, accelerates the photoelectrons to reimage them on the fluorescent screen b, and converts the photoelectron image into a photoimage again. Converted to electrical signals at 10C. An electronic shutter electrode c is enclosed in the image tube 101, and the shutter speed of this electronic shutter is 10 μS at maximum. FIG. 3 is a graph showing the relationship between the opening and closing of the electronic shutter and the flash emission of the light source 6. When the CPU receives the detection signal from the object detector 12 in FIG. 1, the CPU opens the electronic shutter for 10 μS. Then, at the same time when the shutter c is closed, the flash tube of the light source is caused to emit light. In this way, the effective light emission of the flash tube has an area with diagonal lines, and the half-value width of the flash light is about 0.5 μS.
The exposure time can be adjusted by setting the timing of closing the electronic shutter and flashing.

FIG. 4 shows an embodiment in which a Mach-Zehnder type microscopic interferometer is used as an interferometer, and the portion surrounded by a chain line M is the same interferometer. A parallel plane plate P is inserted into one of the two divided light beams to form an image plane. In the above, the same image of the surface of the subject 1 is shifted and overlapped so as to interfere with each other. The other parts corresponding to those of the embodiment shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. In this embodiment, reflected light from the surface of the subject is divided into two images, and these images are overlapped to cause interference, so that the interference pattern does not change due to movement of the subject,
It has the property of being less susceptible to the movement of the subject.

In the present invention, it is sufficient to image the interference pattern along one line. Further, it is easier to adjust the apparatus if the two images are slightly inclined to each other to form overlapping interference fringes and the interference pattern due to the unevenness of the surface to be inspected overlaps the interference fringes. For this purpose, in the embodiment shown in FIG. 1, the optical axis of the objective lens 2 is slightly tilted with respect to the surface to be inspected. In the embodiment shown in FIG. 4, the glass plate G is placed in the optical path of one light beam. The analysis method for processing the image data of the interference pattern to obtain the roughness display value is arbitrary, but an example thereof is Japanese Patent Application No. 60-19408 filed by the present applicant.
No. 9 is shown.

G. Effect Since the roughness measuring device of the present invention has the above-mentioned configuration and is of the interference type, the resolution in the height direction of the unevenness of the surface is high, and the interference pattern is imaged by the exposure for an extremely short time. Therefore, the subject is moving. Can be measured, and surface inspection can be performed without stopping the articles being transferred in the process one by one.

[Brief description of drawings]

FIG. 1 is a side view of an embodiment of the present invention, FIG. 2 is a side view of an interference pattern imaging unit of another embodiment, and FIG. 3 is a time chart of the electronic shutter operation and light emission of the light source in the above embodiment. FIG. 4 is a side view of the third embodiment of the present invention.

Claims (1)

[Claims] 1. Optical means for coherently forming an image of the surface of the subject and an image of the reference surface or the surface of the subject itself.
Means for capturing an interference pattern formed by the superposition of the two images by instantaneous exposure of the surface of the subject and converting it into an electric image signal, and analyzing the image data of the interference pattern obtained by this converting means. And a flash discharge tube for illuminating the electronic shutter and the subject, start of the closing operation of the electronic shutter and start of light emission of the flash tube. And a surface roughness measuring device.